◀ ▲ ▶Branches / Geometry / Elements-euclid / Book--1-plane-geometry / Definition: 1.11: Obtuse Angle

Definition: 1.11: Obtuse Angle

An obtuse angle is one greater than a right angle.

Modern Definition

Euclid's definition corresponds to today's formulation.

Example

The angle \(\angle{RQP}\) (marked light-green) is obtuse.

In the following figure both angles \(\angle{ABC}\) and \(\angle{CBA}\) are obtuse.

Mentioned in:

Axioms: 1
Definitions: 2 3 4
Proofs: 5 6 7
Propositions: 8 9 10

Thank you to the contributors under CC BY-SA 4.0!

Github:

non-Github:

@Calahan

@Casey

@Fitzpatrick

References

Adapted from CC BY-SA 3.0 Sources:

1. Callahan, Daniel: "Euclid’s 'Elements' Redux" 2014

Adapted from (Public Domain)

1. Casey, John: "The First Six Books of the Elements of Euclid"

Adapted from (subject to copyright, with kind permission)

1. Fitzpatrick, Richard: Euclid's "Elements of Geometry"